Hydroelectric generating set runner blade incompleteness simulation method based on CFD and FEM

Abstract

The invention discloses a hydroelectric generating set runner blade incompleteness simulation method based on CFD and FEM, relates to the technical field of safe and stable operation of hydroelectric generating sets, and aims to simulate steady-state operation states of a water turbine under different operation conditions so as to evaluate the influence on the performance of the water turbine under runner blade damage working conditions such as blade wear and fracture. According to the method, important information about the performance and the service life can be provided for design and maintenance of the water turbine, the reliability and safety of a hydroelectric generating set are expected to be improved, meanwhile, the maintenance cost is reduced, and remarkable technical progress is brought to the field of hydroelectric generation.

Description

Technical Field

[0001] The invention relates to the technical field of safe and stable operation of hydropower units, and in particular to a hydropower unit runner blade defect simulation method based on CFD and FEM. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] As a core component of a hydroelectric power station, hydropower units play a vital role in the sustainable generation of electric energy and the stable operation of the power grid. In the design and operation of turbines, they often face complex water flow environments, such as turbulence, vortex, pulsating flow, etc. The surface of the blades may be affected by various external forces, such as water hammer and cavitation. Defects are a reality that blades may face, which may be caused by service life, improper operation or external factors. The presence of defective blades may lead to uneven flow field distribution, affecting the efficiency and stability of the turbine.

[0004] CFD technology provides a tool to deeply understand the interaction between water flow and blades by numerically simulating the flow inside the turbine. By simulating the flow field inside the turbine, the dynamic characteristics, pressure distribution, velocity field and other parameters of the fluid can be analyzed. This provides engineers with an effective means to optimize the design and operation of turbines.

[0005] In actual operation, blades may be damaged for various reasons, and this damage will have a significant impact on the flow field distribution and unit performance. Therefore, in order to more accurately evaluate the impact of damaged blades on turbine performance, a reliable simulation method needs to be established. This simulation method not only needs to consider the direct impact of the damage on fluid flow, but also needs to comprehensively consider its impact on mechanical strength, vibration and pressure.

[0006] The defect simulation method based on CFD introduces conventional geometric models to study the dynamic stress distribution and change law of normal impeller blades and other flow-through components, and analyzes the relationship between transient hydraulic excitation and structural and shaft system responses under fluid-solid coupling. The defective impeller blades are simulated by combining the stress change law of the impeller blades with typical faults, and the defective blade geometric model is constructed. The defective blades designed based on fluid-solid coupling (FEM) are numerically simulated, and the flow field is simulated in CFD software. Such simulations can help engineers understand the specific impact of defects on turbine performance and guide the optimal design and operation strategy of the unit. Summary of the invention

[0007] The purpose of the present invention is to provide a hydropower unit runner blade defect simulation method based on CFD and FEM to address the problems existing in the prior art, aiming to simulate the steady-state operation of the turbine under different operating conditions so as to evaluate the impact of runner blade damage conditions such as blade wear and fracture on the turbine performance.

[0008] The technical solution of the present invention is as follows:

[0009] A CFD and FEM-based simulation method for hydropower unit runner blade defect, comprising:

[0010] Step S1: Obtain basic information of the hydropower unit, determine the normal operating conditions according to the studied hydropower unit, establish a three-dimensional model of the hydropower unit under normal operating conditions, and perform model meshing to provide a physical geometric basis for subsequent steps; the three-dimensional model of the hydropower unit includes: a three-dimensional model of the fluid domain of the hydropower unit and a three-dimensional model of the solid domain of the runner of the hydropower unit;

[0011] Step S2: Based on the constructed three-dimensional model of the fluid domain of the hydropower unit, computational fluid dynamics and dynamic mesh technology are used to obtain the distribution of various physical quantities of the internal flow field under normal operating conditions;

[0012] Step S3: Based on the constructed solid domain three-dimensional model of the hydropower unit runner, the maximum stress value and the maximum pressure value of the runner blade under normal working conditions are obtained by using fluid-solid coupling technology;

[0013] Step S4: Based on the distribution of various physical quantities of the internal flow field under normal working conditions, the maximum stress and pressure values ​​of the runner blades, different types of blade fault models are introduced to design and construct a three-dimensional model of a faulty impeller blade in the fluid domain of a hydropower unit and a three-dimensional model of a faulty impeller blade in the solid domain of a hydropower unit;

[0014] Step S5: Based on the three-dimensional model of the faulty impeller blade in the fluid domain of the hydropower unit, computational fluid dynamics and dynamic mesh technology are used to obtain the distribution of various physical quantities of the internal flow field under the condition of the faulty runner blade;

[0015] Step S6: performing modal calculation on the three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit to obtain the natural frequency and vibration mode characteristics of the faulty runner, and comparing the natural frequency of the wet mode with the hydraulic excitation force frequency to determine the possibility of resonance of the faulty runner;

[0016] Step S7: Based on the distribution of various physical quantities of the internal flow field under the faulty runner blade condition and the natural frequency of the faulty runner, the faulty runner of the hydropower unit is simulated to evaluate the impact of blade wear and fracture on the performance of the turbine, and to prevent and optimize various problems that may arise.

[0017] Furthermore, the three-dimensional model of the hydropower unit is constructed by CATIIA or SpaceClaim software.

[0018] Furthermore, the step S2 comprises:

[0019] In the CFD software Fluent, the flow field of the three-dimensional model of the fluid domain of the hydropower unit is simulated; including: defining the inlet conditions, outlet conditions, and physical properties of the working fluid to simulate the fluid flow inside the hydropower unit; and using computational fluid dynamics and dynamic mesh technology to obtain the distribution of various physical quantities in the internal flow field under normal operating conditions.

[0020] Furthermore, the step S3 comprises:

[0021] The workbench calculation software is used to realize the connection and import of fluid domain calculation data and solid domain data. At the same time, the walls of the solid domain are accurately defined, including the material properties and characteristics of the blades, to ensure the accuracy of the runner components and fluid-solid coupling results.

[0022] Furthermore, the step S4 comprises:

[0023] Based on the distribution of various physical quantities in the internal flow field under conventional working conditions, the CFD-FEM one-way fluid-solid coupling calculation method is used to perform numerical simulation and stress analysis using the Workbench calculation software;

[0024] Establish data samples of faulty blades, use machine learning to automatically detect and classify blade faults, classify faults into different types, and establish a detailed feature library for each type of fault; realize the collection and classification of actual fault conditions of unit blades;

[0025] Combining crack mechanics theory with common crack failures, the blade stress distribution obtained after constructing fluid-solid coupling is constructed to build a crack failure runner model.

[0026] Based on the determined fault type and crack location, a three-dimensional model of the faulty impeller blade in the fluid domain of the hydropower unit and a three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are constructed respectively.

[0027] Furthermore, the step S4 further includes:

[0028] In the process of CFD-FEM unidirectional fluid-solid coupling calculation method, for boundary conditions, the upper crown and main shaft bolts are used to set the joint surface as a fixed constraint, and the centrifugal force, gravity and water pressure load on the fluid-solid coupling surface are considered. The fluid-solid coupling surface includes the blade, the upper crown surface and the lower ring surface, and the upper crown and lower ring gap surface. The water pressure load comes from the flow field pressure data after the CFD unsteady calculation is stabilized; the stress distribution of the blade facing the water surface and the back surface of the water is obtained.

[0029] Furthermore, the blade failure model includes: a wear model, a fatigue crack growth model and a blade fracture model to simulate the possibility of various blade problems.

[0030] Furthermore, the step S6 comprises:

[0031] The natural frequency and vibration mode characteristics of the three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are analyzed. Based on the wet modal calculation method, the Acoustic-Modal calculation software is used to analyze the natural frequency and vibration mode characteristics.

[0032] Furthermore, the step S6 further includes:

[0033] Considering the internal flow field, the fluid domain of the upper crown cavity and the lower ring cavity, the acoustic-solid coupling method is used to perform the wet modal calculation of the working flow channel of the runner; the upper crown bolt sets the joint surface as a fixed constraint, the contact surface between the inner flow channel and the guide vane and the tailwater pipe flow domain is set as a full absorption boundary, the contact surface between the fluid domain and the solid domain is set as a fluid-solid coupling surface, and the rest are rigid wall surfaces; through wet modal calculation, the natural frequency and vibration mode characteristics of the faulty runner are obtained.

[0034] Furthermore, the multiple physical quantities include: streamlines, pressure, pressure pulsation, and speed.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The present invention can conduct multi-dimensional and multi-angle evaluation on the steady-state operation process of faulty impeller blades of hydraulic turbines, fully compare the evaluation under normal conditions of hydraulic turbines with that under crack faults, explore the steady-state operation rules and influences of faulty runner blades, thereby extending the life of hydraulic turbine equipment and maintaining efficient and stable operation of hydropower units.

[0037] 2. The present invention can provide important information about performance and life for the design and maintenance of turbines; it is expected to improve the reliability and safety of hydropower units while reducing maintenance costs, bringing significant technological progress to the field of hydropower generation.

[0038] The present invention can fully consider the influence of faulty runner blades on the internal flow field and the influence of faulty runner blades on the natural frequency and resonance, and effectively ensure the safe and stable operation of the hydropower unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of a simulation method for the defective runner blade of a hydropower unit based on CFD and FEM;

[0040] Figure 2 A schematic diagram of the steps for obtaining modeling data provided by an embodiment of the present invention;

[0041] Figure 3 A schematic diagram of a simulation of a flow field system in a hydropower unit is provided for an embodiment of the present invention;

[0042] Figure 4 A flow chart of a method for simulating crack failure of an impeller blade provided in an embodiment of the present invention;

[0043] Figure 5 A schematic diagram of fluid and solid domain evaluation and analysis of a hydraulic turbine fault model provided by an example of the present invention. DETAILED DESCRIPTION

[0044] It should be noted that relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0045] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0046] Embodiment 1

[0047] As the core equipment of the turbine unit, the safe and stable operation of the turbine runner blades has become a hot topic in the industry. Aiming at the limitations of runner blade fault analysis, the present invention proposes a hydropower unit runner blade defect simulation method based on CFD and FEM according to the conventional operating conditions of the runner blades.

[0048] See also Figure 1-3 A method for simulating the defective blade of a hydropower unit runner based on CFD and FEM specifically comprises the following steps:

[0049] A CFD and FEM-based simulation method for hydropower unit runner blade defect, comprising:

[0050] Step S1: Obtain basic information of the hydropower unit, determine normal operating conditions according to the studied hydropower unit, establish a three-dimensional model of the hydropower unit under normal operating conditions, and perform model meshing, and set boundary layer meshes for the blades to meet the requirements of the turbulence model for boundary mesh size; provide a physical geometric basis for subsequent steps; the three-dimensional model of the hydropower unit includes: a three-dimensional model of the fluid domain of the hydropower unit and a three-dimensional model of the solid domain of the hydropower unit runner; the three-dimensional model of the hydropower unit is a detailed geometric feature including blades and runners. This step involves digitizing the precise three-dimensional geometry of each component of the hydropower unit (including blades and runners) for use in computational fluid dynamics simulations; at the same time, the model meshing is to subdivide the fluid domain inside the hydropower unit into discrete units for numerical simulation;

[0051] It should also be noted that the geometric modeling part involved in step S1, the CAD (computer-aided design) software usually used for modeling the geometric shape of the hydropower unit mainly includes CATIA and SpaceClaim. Although the two have certain differences in user interface, modeling method and integration, in the process of building the geometric model of the hydropower unit, the software and method of model building are selected based on the wide range of functions and complex modeling capabilities of CATIA or the convenience of integrating the model building of SpaceClaim into other CAD software;

[0052] Specifically, in the actual operation process, the specific implementation steps of step S1 are as follows:

[0053] Obtaining basic information of the hydropower unit, determining the type of the hydropower unit according to the basic information, and dividing the working conditions to determine a plurality of different working conditions, and establishing a corresponding three-dimensional model of the hydropower unit under each working condition;

[0054] Based on the research target turbine, 3D scanning of turbine impeller blades is performed. The scanned parts include runner blades (2 blades), lower ring, upper crown, discharge cone, etc. To meet the simulation calculation requirements, adjustments can be made during the actual execution.

[0055] According to the 3D scanning data and CAD drawings, the modeling software CATIA is used to model the three-dimensional fluid domain, including the volute, movable guide vanes, fixed guide vanes, runner, tailwater pipe and upper and lower gap fluid domains. The solid domain of the runner structure is also modeled, that is, the three-dimensional model of the fluid domain of the hydropower unit and the three-dimensional model of the solid domain of the hydropower unit runner are obtained;

[0056] In a possible implementation, basic information of the hydropower unit is obtained, and the operating conditions of the hydropower unit are divided according to the basic information to determine a plurality of different operating conditions, including:

[0057] Obtain basic information of the hydropower unit, including the minimum water head Hmin , Maximum head H max , no-load opening Y 空载 And full opening Y max ;

[0058] Combined with the conventional operating conditions of the hydropower unit, the optimal water head H and the optimal opening Y within the interval are determined to determine the optimal operating conditions of the turbine unit simulation;

[0059] In the selected implementation, a corresponding three-dimensional model of the hydropower unit is established under the optimal operating conditions, including: establishing a three-dimensional model of the hydropower unit including a volute, fixed guide vanes, movable guide vanes, a runner and a tailwater pipe under each operating condition.

[0060] like Figure 2 As shown, this embodiment provides a method for acquiring data of a three-dimensional model of a hydropower unit;

[0061] It is necessary to scan the runner model of the water turbine unit in the target hydropower unit, and build the model in combination with the drawings of other components such as the water turbine runner. For the data acquisition method of the runner blades, a 3D scanner is used for data collection, and a 3D laser scanner is used for data supplementary scanning to obtain point cloud data;

[0062] The scanned point cloud is preprocessed, including point cloud registration, data noise reduction, and thinning. When there are abnormal points and isolated points that are out of the scan target in the point cloud data, filtering or human-computer interaction can be used for noise reduction. In order to ensure the accuracy of subsequent point cloud processing, noise reduction must be done carefully. Point cloud data thinning should be performed without affecting the identification and extraction of blade feature points. This part of the work should be handled with caution. When the computer computing power meets the requirements, the thinning work should be minimized.

[0063] The scanned point cloud is registered to the coordinate system established by the key points, and the least squares method is used for registration through the same-name points;

[0064] Create triangular facets based on the registered point cloud, and then perform precise surface fitting to form a model; perform accuracy analysis on the established model. If the accuracy does not meet the requirements, re-analysis and processing is required;

[0065] The established model is integrated with the known structural model to provide basic model data for three-dimensional simulation calculations.

[0066] Step S2: Based on the constructed three-dimensional model of the fluid domain of the hydropower unit, computational fluid dynamics and dynamic mesh technology are used to obtain the distribution of various physical quantities of the internal flow field under normal operating conditions; wherein the steady-state operating conditions of the conventional hydropower unit in step S2 need to be combined with the actual unit data, and the inlet and outlet speeds and other conditions need to be set to ensure the accuracy of data simulation under fault-free conditions;

[0067] In this embodiment, specifically, step S2 includes:

[0068] In the CFD software Fluent, the flow field of the three-dimensional model of the fluid domain of the hydropower unit is simulated; including: defining the inlet conditions, outlet conditions, and physical parameters of the working fluid to simulate the fluid flow inside the hydropower unit; and using computational fluid dynamics and dynamic mesh technology to obtain the distribution of various physical quantities in the internal flow field under normal operating conditions;

[0069] In this embodiment, the step S2 simulates the flow field of the hydroelectric unit based on CFD software (Fluent). This includes defining parameters such as inlet conditions, outlet conditions, and physical properties of the working fluid to simulate the fluid flow inside the turbine in the hydroelectric unit, and using computational fluid dynamics and dynamic grid technology to obtain the distribution of physical quantities such as internal flow field streamlines, pressure, pressure pulsation, and speed under normal operating conditions. This step is a key numerical simulation process, which includes using CFD software to establish a three-dimensional fluid flow field model inside the turbine, taking into account multiple parameters such as inlet flow velocity, temperature, turbulence model, blade surface friction, etc., to simulate the behavior of the turbine under normal steady-state operating conditions.

[0070] Step S3: Based on the constructed solid domain three-dimensional model of the hydropower unit runner, the fluid-solid coupling technology is used to obtain the maximum stress value and the maximum pressure value of the runner blade under normal working conditions; wherein the fluid-solid coupling calculation in step S3 needs to clarify the material properties and characteristics of the blades and other components in the solid domain to ensure the accuracy of the runner components and the fluid-solid coupling results;

[0071] In this embodiment, specifically, step S3 includes:

[0072] The workbench calculation software is used to realize the connection and import of fluid domain calculation data and solid domain data. At the same time, the walls of the solid domain are accurately defined, including the material properties and characteristics of the blades, to ensure the accuracy of the runner components and fluid-solid coupling results.

[0073] That is, in this embodiment, step S2 and step S3 are based on the three-dimensional model of the hydropower unit under the optimal operating conditions, and use computational fluid dynamics, dynamic mesh technology and fluid-solid coupling technology to obtain the distribution of multiple physical quantities, the maximum runner stress and the maximum blade pressure in the conventional steady-state process under the optimal operating conditions, including: simulating and calculating the distribution of physical quantities such as internal flow field streamlines, pressure, pressure pulsation, and speed under the conventional operating conditions of the three-dimensional model of the hydropower unit, and the maximum runner blade stress and the maximum blade pressure under conventional conditions.

[0074] In fact, no matter how complex the turbulent flow is, the basic equations of turbulence are still the continuity equation, momentum equation and energy equation, which are as follows in order.

[0075]

[0076]

[0077] In the formula, u i is the fluid velocity at coordinate x i directional component; ρ is the fluid density; t is the time; p is the static pressure; S mi is a custom source term, including gravity and the interaction between multiphase flows; τ ij is the stress tensor; h tot is the total specific enthalpy; e is the internal energy; k eff is the effective heat transfer coefficient; T is the temperature.

[0078] In the relevant research on three-dimensional simulation of hydraulic turbines, the standard k-ε turbulence model can well simulate the flow field inside the turbine. Therefore, the turbulence model selected in the present invention is the standard k-ε turbulence model. The standard k-ε turbulence model introduces the transport equation about turbulent kinetic energy k and dissipation rate ε, and calculates the turbulent kinetic energy viscosity μ through k and ε. i , which belongs to the two-equation model. The transport equations for turbulent kinetic energy k and dissipation rate ε are as follows:

[0079]

[0080] In the formula, G k is the generation term of turbulent kinetic energy k caused by the mean velocity gradient; G b is the term for the turbulent kinetic energy k caused by buoyancy; C 1ε , C 2ε and C 3ε is an empirical constant; σ k and σ kε is the Prandtl number corresponding to the turbulent kinetic energy k and the dissipation rate ε; S k and S ε It is a user-defined source item.

[0081] In this model, the turbulent kinetic energy dissipation rate ε is defined as:

[0082]

[0083] The characteristic velocity is the turbulent kinetic energy k, the characteristic length scale is the dissipation rate ε, and the relationship between the two reflects the turbulent viscosity μ t :

[0084]

[0085] like Figure 3 As shown, a simulation model of the flow field system inside the hydropower unit is constructed to obtain the distribution of physical quantities such as streamlines, pressure, pressure pulsation, and speed under steady-state conditions of a normally operating hydro-turbine unit;

[0086] According to the 3D scanning data and CAD drawings, the modeling software CATIA is used to model the three-dimensional fluid domain, including the volute, movable guide vanes, fixed guide vanes, runner, draft tube, and upper and lower gap fluid domains;

[0087] For the three-dimensional model meshing, the meshing of the CFD calculation model should ensure the orthogonality of the mesh as much as possible, and reduce the number of calculation nodes as much as possible under the premise of ensuring the calculation accuracy, so as to reduce the calculation workload. The calculation model meshing tool of this project uses ANSYS ICEM to perform CFD meshing on the flow field such as the volute, runner, movable guide vanes, fixed guide vanes, upper and lower gaps and tailwater pipes. The wedge mesh is used in the guide vane area, and the other parts are hexahedral structured meshes. The runner blades are set with boundary layer meshes to meet the requirements of the turbulence model for the boundary mesh size;

[0088] Based on Fluent computing software, 1D-3D partially overlapping coupled numerical simulation is performed; for the setting of boundary conditions, the volute inlet and tailwater pipe outlet are coupled with the one-dimensional pipeline, and the interfaces of each fluid domain are connected by interface pairs. The rotating domain is set to Frame Motion during steady calculations and Mesh Motion during unsteady calculations, and the guide vanes are opened by dynamic mesh technology. The actions of the guide vanes and runners are controlled by Fluent UDF; for the flow model, the DES turbulence model is used to simulate turbulence. For steady-state and transient calculations, the pressure-based separation iterative algorithm is used for solution, and the SIMPLEC algorithm is used to achieve iterative solution of the velocity field and pressure field. The momentum, turbulent kinetic energy and its dissipation rate are all calculated using the second-order upwind format; for the time step, the transient calculation time step of the startup process is 0.001s, corresponding to the time for the runner to rotate 3° at the rated speed, and each calculation time step has a maximum of 30 iterations;

[0089] The three-dimensional numerical simulation method of the turbine unit is verified through grid independence verification. The grid independence verification uses multiple sets of grids with different degrees of refinement, takes the rated working condition and no-load working condition of the turbine as the object, and verifies with macro parameters (flow, torque) and pressure pulsation of important areas (bladeless area, blade inlet) as reference values. The error of two consecutive solutions is between 5% and 10%. It is generally believed that the influence of the grid on the result is within an acceptable range. The verification is completed, and the number of fluid grids suitable for CFD calculation is selected by comparison;

[0090] Based on the optimal steady-state operation condition of the turbine unit, the speed and guide vane opening are kept unchanged, and the three-dimensional flow field and pressure pulsation characteristics of the unit under steady-state operation are studied;

[0091] Based on the steady-state operation results of the turbine under the optimal working condition, the internal flow field analysis is carried out, including the distribution of physical quantities such as streamlines, pressure, pressure pulsation, velocity, cavitation, etc., and a comprehensive study is conducted from the aspects of space, time domain and frequency domain. In order to obtain the spatial distribution and propagation characteristics of various physical quantities in the turbine flow channel during the startup process, multiple measuring points need to be arranged in the volute, guide vane, runner, draft tube, and gap to obtain the pressure pulsation characteristics of the entire flow channel. In view of the time domain and frequency domain characteristics, in order to accurately identify and distinguish the physical time domain characteristics of the pressure pulsation at each measuring point, a strategy combining multiple methods is adopted. Through the fast Fourier transform (FFT), the information of various frequencies is identified and obtained in the entire time range. The empirical mode decomposition (EMD) method is used to decompose the pressure pulsation time domain signal into a series of intrinsic mode functions with different frequencies. At the same time, the short-time Fourier transform (STFT) is introduced to realize the time-frequency characteristic analysis of the pressure pulsation signal.

[0092] Step S4: Based on the distribution of various physical quantities of the internal flow field under normal working conditions, the maximum stress and pressure values ​​of the runner blades, different types of blade fault models are introduced to design and construct a three-dimensional model of a faulty impeller blade in the fluid domain of a hydropower unit and a three-dimensional model of a faulty impeller blade in the solid domain of a hydropower unit;

[0093] In this embodiment, specifically, step S4 includes:

[0094] Based on the distribution of various physical quantities in the internal flow field under conventional working conditions, the CFD-FEM one-way fluid-solid coupling calculation method is used to perform numerical simulation and stress analysis using the Workbench calculation software;

[0095] Establish data samples of faulty blades, use machine learning to automatically detect and classify blade faults, classify faults into different types, and establish a detailed feature library for each type of fault; realize the collection and classification of actual fault conditions of unit blades;

[0096] Combining crack mechanics theory with common crack failures, the blade stress distribution obtained after constructing fluid-solid coupling is constructed to build a crack failure runner model.

[0097] Based on the determined fault type and crack location, a three-dimensional model of the faulty impeller blade in the fluid domain of the hydropower unit and a three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are constructed respectively;

[0098] The blade failure model includes: a wear model, a fatigue crack growth model and a blade fracture model to simulate the possibility of various blade problems. In this step, different types of blade failure models simulate various possible problems of the blade, such as blade surface wear, crack growth or complete fracture;

[0099] That is, step S4 is to design a faulty impeller blade model of a hydropower unit in combination with the location of the maximum stress of fluid-solid coupling and the types of crack failures that often occur in actual working conditions, and to perform three-dimensional faulty blade fluid domain modeling and three-dimensional runner blade structure solid domain fault modeling based on 3D scanning data and CATIA;

[0100] In this embodiment, specifically, step S4 further includes:

[0101] In the process of CFD-FEM unidirectional fluid-solid coupling calculation method, for boundary conditions, the upper crown and main shaft bolts are used to set the joint surface as a fixed constraint, and the centrifugal force, gravity and water pressure load on the fluid-solid coupling surface are considered. The fluid-solid coupling surface includes the blade, the upper crown surface and the lower ring surface, and the upper crown and lower ring gap surface. The water pressure load comes from the flow field pressure data after the CFD unsteady calculation is stabilized; the stress distribution of the blade facing the water surface and the back surface of the water is obtained.

[0102] like Figure 4 As shown, this embodiment provides a method for constructing a three-dimensional fault model of a hydropower unit by combining a three-dimensional model stress analysis with a typical impeller blade crack fault condition, which is specifically as follows:

[0103] Based on the information of internal flow field physical quantities, the CFD-FEM one-way fluid-solid coupling calculation method is performed using Workbench calculation software. For boundary conditions, the upper crown and main shaft bolts are used to set the joint surface as a fixed constraint, and the centrifugal force, gravity and water pressure load on the fluid-solid coupling surface are considered. The fluid-solid coupling surface includes the blade, the upper crown surface and the lower ring surface, and the upper crown and lower ring gap surface. The water pressure load comes from the flow field pressure data after the CFD unsteady calculation is stabilized. Obtain the stress distribution of the blade facing the water and the back of the water;

[0104] Establish data samples of faulty blades, use machine learning to automatically detect and classify blade faults, classify faults into different types, such as fatigue cracks, deformation, material wear, etc., and establish a detailed feature library for each type of fault. Realize the collection and classification of actual fault conditions of unit blades;

[0105] Combining crack mechanics theory with common crack failures, the crack failure runner model is constructed according to the blade stress distribution obtained after the fluid-solid coupling model is constructed.

[0106] Based on the determination of the fault type and the crack location, a three-dimensional model of the faulty impeller blade in the fluid domain of the hydropower unit and a three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are constructed respectively.

[0107] Step S5: Based on the three-dimensional model of the impeller blade with fault in the fluid domain of the hydropower unit, computational fluid dynamics and dynamic mesh technology are used to obtain the distribution of various physical quantities of the internal flow field under the condition of the faulty runner blade; and to study how the blade fault affects the operating stability of the turbine under different operating conditions, including changes in blade vibration, noise, pressure pulsation, etc. In this step, the performance and stability of the turbine are evaluated by comparing the CFD simulations under different operating conditions, taking into account the impact of blade defects on fluid flow, as well as changes in mechanical vibration, acoustic characteristics, etc.

[0108] Step S6: performing modal calculation on the three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit to obtain the natural frequency and vibration mode characteristics of the faulty runner, and comparing the natural frequency of the wet mode with the hydraulic excitation force frequency to determine the possibility of resonance of the faulty runner;

[0109] In this embodiment, specifically, step S6 includes:

[0110] The natural frequency and vibration mode characteristics of the three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are analyzed, and the natural frequency and vibration mode characteristics are analyzed using the Acoustic-Modal calculation software based on the wet modal calculation method; wherein the fault simulation in step S6 not only includes simulating the operating state of the flow field in the turbine, but also considers the changes in the natural frequency and vibration mode characteristics caused by the faulty runner;

[0111] Considering the internal flow field, the fluid domain of the upper crown cavity and the lower ring cavity, the acoustic-solid coupling method is used to calculate the wet modal of the working flow channel of the runner; the upper crown bolt sets the joint surface as a fixed constraint, the contact surface between the internal flow channel and the guide vane and the tailwater pipe flow domain is set as a full absorption boundary, the contact surface between the fluid domain and the solid domain is set as a fluid-solid coupling surface, and the rest are rigid wall surfaces; through wet modal calculation, the natural frequency and vibration mode characteristics of the faulty runner are obtained;

[0112] The various physical quantities include: streamline, pressure, pressure pulsation, and speed.

[0113] That is, step S5 is to perform three-dimensional fluid domain meshing on the faulty blade, and use FLUENT calculation software to obtain the distribution of physical quantities such as internal flow field streamlines, pressure, pressure pulsation, velocity, cavitation, etc. during the operation of the faulty impeller blade;

[0114] Step S6 is to perform FEM calculation meshing of the solid domain runner structure of the faulty blade, import the steady-state operating condition, and use the Workbench calculation software to perform CFD-FEM one-way fluid-solid coupling calculation. The analysis of the dynamic stress of the faulty runner blade in the steady-state process includes spatial, time domain, frequency domain and other aspects, providing support for the evaluation of the runner operation status and optimized operation.

[0115] Step S7: Based on the distribution of various physical quantities of the internal flow field under the working condition of the faulty runner blade and the natural frequency of the faulty runner, the faulty runner of the hydropower unit is simulated to evaluate the impact of blade wear and fracture on the performance of the turbine, and to prevent and optimize various problems that arise; that is, the above-mentioned simulation results are analyzed in detail to evaluate the impact of blade wear and fracture on the performance of the turbine. This includes the evaluation of parameters such as flow velocity distribution, blade force distribution, turbine efficiency, and pressure pulsation in the blade defect area. The frequency vibration mode characteristics of the faulty blade model are analyzed to avoid the possibility of resonance, which is used for turbine design and maintenance to provide important information about performance and life, thereby improving the reliability and safety of the hydropower unit and reducing maintenance costs; through in-depth analysis of the simulation results, quantitative and qualitative insights into the impact of blade defects on turbine performance can be obtained, helping designers and maintenance personnel to better understand the behavior of the turbine and take necessary measures;

[0116] That is Figure 5 As shown, the fault model fluid domain and solid domain are analyzed to construct the evaluation analysis of the fault model of the hydraulic turbine unit;

[0117] The three-dimensional flow field pressure pulsation analysis and time domain and frequency domain characteristic analysis of the water body failure model of the turbine unit are carried out to obtain the state of each physical quantity of the internal flow field, and to explore the various changes and impacts of the internal flow field of the turbine unit after the crack failure occurs;

[0118] The natural frequency and vibration mode characteristics of the solid domain model of the turbine unit are analyzed. Based on the wet modal calculation method, the Acoustic-Modal calculation software is used to analyze the natural frequency and vibration mode characteristics. At the same time, the internal flow field, the fluid domain of the upper crown cavity and the lower ring cavity are considered, and the acoustic-solid coupling method is used to perform the wet modal calculation of the working flow channel of the runner. The upper crown bolt sets the joint surface as a fixed constraint, the contact surface between the internal flow channel and the guide vane and the tailwater pipe flow domain is set as a full absorption boundary, the contact surface between the fluid domain and the solid domain is set as a fluid-solid coupling surface, and the rest are rigid walls;

[0119] The natural frequency and vibration mode characteristics of the faulty runner can be obtained through modal calculation. When the external force frequency is close to the natural frequency of the structure, and the vector direction coincides with the vibration mode direction of the structure, the structure will resonate. Calculate the natural frequencies and vibration modes of the first 10 orders, compare the natural frequencies of the wet modes with the frequencies of hydraulic excitation forces such as dynamic and static interference and blade vortex, determine whether there is a possibility of resonance under the corresponding operating conditions, and use the vibration mode to determine the vibration form when resonance occurs;

[0120] The percentage difference between the hydraulic excitation force frequency and the impeller natural frequency is called margin M, which is used to characterize the possibility of impeller resonance. The calculation formula is as follows. According to engineering experience, when M does not exceed 20%, the impeller is more likely to resonate.

[0121]

[0122] Where: f N is the Nth order natural frequency of the impeller, where the wet mode after acoustic-solid coupling is considered (Hz); f is the hydraulic excitation frequency (Hz).

[0123] The time history changes and frequency characteristics of the faulty runner are studied and analyzed to obtain the similarities and differences between the runner stress under fault conditions and normal conditions, so as to provide guidance for evaluating whether the turbine runner should continue to operate under fault conditions and provide technical support for operation decision-making;

[0124] The fault model analysis is mainly carried out from two aspects: flow field and structural field. For the flow field, the focus is on the unstable hydraulic excitation phenomenon caused by the faulty blade, including the aforementioned blade vortex, Karman vortex, dynamic and static interference, and the pressure pulsation between the flow-passing components and the axial force and radial force, and the flow field characteristics of the turbine are compared without faults; for the structural field, the focus is on the stress concentration part of the runner, the stress-strain time domain process and other characteristics, and it is judged whether the runner resonates under fault conditions; at the same time, the multivariate correlation between the faulty runner obtained by simulation calculation and the calculated physical field quantities (such as pressure, pressure pulsation, main shaft torque, etc.) and various typical hydraulic phenomena is analyzed and studied, and the influence of crack faults on various influencing factors is quantitatively analyzed.

[0125] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0126] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A method for simulating the defect of a hydropower unit runner blade based on CFD and FEM, characterized in that: include: Step S1: Obtain basic information of the hydropower unit, determine the normal operating conditions according to the studied hydropower unit, establish a three-dimensional model of the hydropower unit under normal operating conditions, and perform model meshing to provide a physical geometric basis for subsequent steps; The three-dimensional model of the hydroelectric generator unit includes: a three-dimensional model of the fluid domain of the hydroelectric generator unit and a three-dimensional model of the solid domain of the runner of the hydroelectric generator unit; Step S2: Based on the constructed three-dimensional model of the fluid domain of the hydropower unit, computational fluid dynamics and dynamic mesh technology are used to obtain the distribution of various physical quantities of the internal flow field under normal operating conditions; Step S3: Based on the constructed solid domain three-dimensional model of the hydropower unit runner, the maximum stress value and the maximum pressure value of the runner blade under normal working conditions are obtained by using fluid-solid coupling technology; Step S4: Based on the distribution of various physical quantities of the internal flow field under normal working conditions, the maximum stress and pressure values ​​of the runner blades, different types of blade fault models are introduced to design and construct a three-dimensional model of a faulty impeller blade in the fluid domain of a hydropower unit and a three-dimensional model of a faulty impeller blade in the solid domain of a hydropower unit; Step S5: Based on the three-dimensional model of the faulty impeller blade in the fluid domain of the hydropower unit, computational fluid dynamics and dynamic mesh technology are used to obtain the distribution of various physical quantities of the internal flow field under the condition of the faulty runner blade; Step S6: performing modal calculation on the three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit to obtain the natural frequency and vibration mode characteristics of the faulty runner, and comparing the natural frequency of the wet mode with the hydraulic excitation force frequency to determine the possibility of resonance of the faulty runner; Step S7: Based on the distribution of various physical quantities of the internal flow field under the faulty runner blade condition and the natural frequency of the faulty runner, the faulty runner of the hydropower unit is simulated to evaluate the impact of blade wear and fracture on the performance of the turbine, and to prevent and optimize various problems that may arise.

2. The method for simulating the defect of a hydropower unit runner blade based on CFD and FEM according to claim 1 is characterized in that: The three-dimensional model of the hydropower unit is constructed by using CATIIA or SpaceClaim software.

3. The method for simulating the defect of a hydropower unit runner blade based on CFD and FEM according to claim 1 is characterized in that: The step S2 comprises: In the CFD software Fluent, the flow field of the three-dimensional model of the fluid domain of the hydropower unit is simulated; including: defining the inlet conditions, outlet conditions, and physical properties of the working fluid to simulate the fluid flow inside the hydropower unit; and using computational fluid dynamics and dynamic mesh technology to obtain the distribution of various physical quantities in the internal flow field under normal operating conditions.

4. The method for simulating the defective blades of a hydropower unit based on CFD and FEM according to claim 1 is characterized in that: The step S3 comprises: The workbench calculation software is used to realize the connection and import of fluid domain calculation data and solid domain data. At the same time, the walls of the solid domain are accurately defined, including the material properties and characteristics of the blades, to ensure the accuracy of the runner components and fluid-solid coupling results.

5. The method for simulating the defect of a hydropower unit runner blade based on CFD and FEM according to claim 1 is characterized in that: The step S4 comprises: Based on the distribution of various physical quantities in the internal flow field under conventional working conditions, the CFD-FEM one-way fluid-solid coupling calculation method is used to perform numerical simulation and stress analysis using the Workbench calculation software; Establish data samples of faulty blades, use machine learning to automatically detect and classify blade faults, classify faults into different types, and establish a detailed feature library for each type of fault; realize the collection and classification of actual fault conditions of unit blades; Combining crack mechanics theory with common crack failures, the blade stress distribution obtained after constructing fluid-solid coupling is constructed to build a crack failure runner model. Based on the determined fault type and crack location, a three-dimensional model of the faulty impeller blade in the fluid domain of the hydropower unit and a three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are constructed respectively.

6. The method for simulating the defective blades of a hydropower unit based on CFD and FEM according to claim 5 is characterized in that: The step S4 further includes: In the process of CFD-FEM unidirectional fluid-solid coupling calculation method, for boundary conditions, the upper crown and main shaft bolts are used to set the joint surface as a fixed constraint, and the centrifugal force, gravity and water pressure load on the fluid-solid coupling surface are considered. The fluid-solid coupling surface includes the blade, the upper crown surface and the lower ring surface, and the upper crown and lower ring gap surface. The water pressure load comes from the flow field pressure data after the CFD unsteady calculation is stabilized; the stress distribution of the blade facing the water surface and the back surface of the water is obtained.

7. The method for simulating the defect of a hydropower unit runner blade based on CFD and FEM according to claim 1 is characterized in that: The blade failure model includes: a wear model, a fatigue crack growth model and a blade fracture model to simulate the possibility of various blade problems.

8. The method for simulating the defective blades of a hydropower unit based on CFD and FEM according to claim 1 is characterized in that: The step S6 comprises: The natural frequency and vibration mode characteristics of the three-dimensional model of the faulty impeller blade in the solid domain of the hydropower unit are analyzed. Based on the wet modal calculation method, the Acoustic-Modal calculation software is used to analyze the natural frequency and vibration mode characteristics.

9. The method for simulating defective blades of a hydropower unit based on CFD and FEM according to claim 8 is characterized in that: The step S6 further includes: Considering the internal flow field, the fluid domain of the upper crown cavity and the lower ring cavity, the acoustic-solid coupling method is used to perform the wet modal calculation of the working flow channel of the runner; the upper crown bolt sets the joint surface as a fixed constraint, the contact surface between the inner flow channel and the guide vane and the tailwater pipe flow domain is set as a full absorption boundary, the contact surface between the fluid domain and the solid domain is set as a fluid-solid coupling surface, and the rest are rigid wall surfaces; through wet modal calculation, the natural frequency and vibration mode characteristics of the faulty runner are obtained.

10. The method for simulating the defect of a hydropower unit runner blade based on CFD and FEM according to claim 1, characterized in that: The various physical quantities include: streamline, pressure, pressure pulsation, and speed.

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